The present invention relates to a self-adapting method of controlling titre in an injection unit for an internal combustion engine.
As is known, the majority of vehicles commercially available at present are fitted with injection units provided with systems for controlling titre which are adapted to regulate the quantity of fuel to be supplied to each individual cylinder in order to obtain an exhaust titre which is as close as possible to an objective titre.
Some of these control systems are of the self-adapting type, i.e. they are able to offset the output dispersions that cause the engine and the exhaust unit to move away from the nominal case set at the time of calibration and also partially to offset variations due to the ageing of the components of the engine and the exhaust unit, in particular the oxygen sensors and the catalytic system.
Control systems are known, for instance, which comprise a first and a second oxygen sensor disposed respectively upstream and downstream of the catalytic system. The information supplied by the sensor disposed upstream of the catalytic system is used to calculate a correction coefficient for a theoretical quantity of fuel to be injected into each cylinder such that the titre output from the combustion chamber, upstream of the catalytic system, is equal to an objective titre, while the information supplied by the sensor disposed downstream of the catalytic system is used to apply further corrections to the control parameters calculated on the basis of the information supplied by the sensor upstream of the catalytic system. On the basis of the information from the sensor disposed downstream of the catalytic system, an additional coefficient may in particular be calculated which modifies the value of the objective titre.
These known solutions have, however, a drawback due to the intrinsic slowness of adaptation and do not make it possible to obtain information on the functional nature of the injection control system, in particular on the oxygen sensors, which can be obtained only by using further sensors.
The object of the present invention is to provide a method which is free from the above-mentioned drawbacks and which, in particular, enables high-speed adaptation.
The invention therefore relates to a self-adapting method of controlling titre for an internal combustion engine 2 provided with a system for reducing pollutant emissions 4 and first and second sensor means of stoichiometric composition 5 disposed respectively upstream and downstream of this system for reducing pollutant emissions 4 and adapted to generate an upstream composition signal V1 and respectively a downstream composition signal V2, this method comprising the stages of:
determining a correction coefficient KO2 as a function of the upstream composition signal V1, the downstream composition signal V2 and an objective signal Vxc2x0 indicative of an objective exhaust titre;
a) determining an operating quantity of fuel QF to be injected into each cylinder of the engine 2 as a function of the correction coefficient KO2;
characterised in that it further comprises the stages of:
b) storing a plurality of current values VAC(i, j) of an adaptation signal VA, each associated with a respective combination of values of the number of revolutions RPM and the load L of the engine 2;
c) updating these current values VAC(i, j) as a function of this downstream composition signal V2;
d) selecting, on each engine cycle, a current value VAC(i, j) corresponding to the number of revolutions RPM and the load L of the engine 2 in this engine cycle;
e) generating this adaptation signal VA as a function of the current value VAC(i, j) selected;
and in that the stage a) comprises the stage of:
al) determining the correction coefficient KO2 also as a function of this adaptation signal VA.